Field of the Invention
The prevent disclosure relates to power conversion for a renewable energy site. More particularly, the present disclosure relates to a hybrid power converter system that is configured to provide connections of three different power buses together. The power buses may include a power bus for a DC power source, a power bus for an AC load, and a power bus for an energy storage unit. Embodiments of the disclosure may also include a renewable energy site comprising the hybrid power converter system and a method of energy conversion at a renewable energy site.
Description of Related Art
By way of background, the following patents and patent applications are each hereby incorporated by reference in their entireties: Chinese Patent Application Nos. CN 102769302 and CN 103296695; Japanese Patent Application No. JP 2012075224; Korean Patent Application Nos. KR 20110014027, KR 20120110478, and KR 20130138611; Taiwanese Patent Application No. TW 201328101; U.S. Patent Application Nos. US 20090189445, US 20110095606, US 20110137481, US 20120013190, US 20120013192, US 20120313436, US 20130051105, US 20130234521, and US 20130328397; U.S. Pat. No. 7,411,308, U.S. Pat. No. 8,344,550, and U.S. Pat. No. 8,482,155; and PCT Application Nos. WO 2013004067 and WO 2007018830.
Renewable energy sources like solar power plants are subject to unpredictable power output due to changes in the environment in their vicinity. Chief among these are the movement of clouds which can rapidly cause their power output to fluctuate. As the percentage of power from such plants supplied to the public power grid increases the severity of the problem also increases. Recently, power utilities are demanding that new solar power plants be designed with features to prevent their output from changing faster than a specified rate.
There are two methods to meet these new requirements. The first and most common approach is to include some type of energy storage or generation capability within the scope of the power plant. These include battery systems or diesel generators which can supplement the power produced by the plant when cloud events occur such that the power output remains within the required specifications. While technically straightforward this approach severely affects the economic viability of the project due to the high cost of the storage element or resistance to application of diesel generators. The second and less common approach is to forecast weather in such a way that the output of the plant can be gradually changed in advance of when cloud cover would appear. The above methods can be applied independently or in combination in varying degrees.
Previous approaches of the power storage method have required some form of power conversion. Power conversion allows power flow from power sources and loads which have much different characteristics. In particular, voltage and frequency often do not match between a power source and a power load. In addition, different loads may have different characteristics. In systems with three power buses, typically two power converters must be applied to connect the three buses- one converter to convert power between the renewable source and the AC grid and a second converter between the AC grid and the energy storage element, often a battery bank. One problem with this approach is that it requires two converters and the infrastructure to connect them to the AC grid. This effectively doubles the cost of the converter hardware. Thus, there is a need in the art for improved systems and methods for power conversion at renewable energy sites.